After about 90 minutes of debate, Assembly Democrats were three votes short of the 54 needed to override the veto. Speaker Vincent Prieto (D., Hudson) did not record an official vote and said he would try "again and again" to defeat the veto.

Christie, a Republican running for president, preserved his record of sustaining each of the 50 some vetoes Democrats have tried to override. (He has vetoed dozens of other bills that Democrats have not tried to defeat.)

The bill, which the Assembly passed on a 74-0 vote in June, would make it more difficult for certain people with a history of mental illness to expunge such records for the purpose of buying a firearm.

It would require individuals previously committed to a mental institution to notify law enforcement of their intent to expunge their mental health records, which show up in the national criminal background check system that licensed dealers are required to consult before selling a gun.

The Senate also voted unanimously in June in favor of the legislation.

Judges are required to grant expungement if they determine the petitioner is not likely to present a threat to the public.

The courts had supported the bill, saying law enforcement was best qualified to assess whether an individual seeking expungement posed a risk to public safety.

Some Democrats invoked the mass shooting Wednesday in San Bernardino, Calif., in which at least 14 people were killed at a services center for the disabled, even as lawmakers acknowledged they weren't sure the bill could have prevented such an incident.

"I didn't come here for a moment of silence," Assemblyman Reed Gusciora (D., Mercer) said. "I came here for a moment of action."

Republicans argued that Christie had exposed a loophole in the bill: An individual could seek to expunge his mental health record without informing a judge that he intended to buy a gun. Then, once that record was erased, the person could go buy a gun undetected, Republicans argued.

"It's not even a question that those people are going to fall through the cracks," said Assemblyman Anthony Bucco (R., Morris).

Assemblyman Joe Lagana (D., Bergen) said this argument was flawed. He noted that firearms applicants must consent to a mental-health record search by the state police.

Applicants are required to sign a form that says they "consent to the disclosure of my mental health records, including disclosure of the fact that said records may have been expunged, to the Chief of Police and the Superintendent of State Police, or their designees, for the purpose of verifying my firearms permit application and my fitness to own a firearm."

Therefore, the authorities would catch anyone who tried to game the system, Lagana said. "There really is no loophole," he said.

Reached late Thursday, a spokeswoman for the Administrative Office of the Courts said the office's experts weren't available to comment.

Christie vetoed the bill in August, saying he could not "endorse a continued path of patchwork proposals and fragmented statutes that add further confusion to an already cumbersome area of law."

Instead, he said, the state should focus on overhauling its mental-health system. He returned the bill to the Legislature with his recommendations. In October, three Senate Republicans joined the chamber's 24 Democrats to override Christie's veto, marking the first time either house of the Legislature had achieved that feat during the governor's tenure.

That vote seemed to signal a possible paradigm shift in Trenton, after years in which Republicans reversed their votes on various measures following Christie's vetoes to stay in line with the governor.

And November's Assembly elections, in which Democrats picked up four seats, confirmed to some analysts that Republicans needed to break with the deeply unpopular Christie.

The Democratic majority will expand when a new legislative session begins in mid-January.

The voting session came a day after Assemblyman Gilbert "Whip" Wilson, a Camden Democrat, abruptly resigned from the Legislature. Wilson was to be sworn in as Camden County sheriff on Thursday, and state law prohibits people from simultaneously holding two elected offices.

On Thursday, four Republicans -- including Chris A. Brown (R., Atlantic) and Jack Ciattarelli (R., Somerset), both in competitive districts -- joined the chamber's 47 Democrats to vote in favor of the override. Assemblyman Jay Webber (R., Morris) and Assemblywoman Amy Handlin (R., Monmouth) also voted in favor.

The unofficial vote was 51-17, with 11 abstentions.

Even some who voted against it expressed unease.

"This was a 74-0 vote. And I voted yes," said Assemblywoman BettyLou DeCroce (R., Morris). "So am I very disturbed and bothered over this? Indeed I am. Am I bothered that the administration didn't guide us better on what they felt was missing? I'm very bothered."

Ultimately, though, she said she preferred Christie's approach. She and other Republicans also suggested Democrats were hoping to deal Christie a political blow.

Even if Christie's proposal was better, Democrats said, it had not gone through the committee process to be vetted.

Concurring with Christie's conditional veto on Thursday would have represented the "antithesis of the thoughtful process we're supposed to undergo in this chamber," said Assemblyman John S. Wisniewski (D., Middlesex).

Gov. Christie on Tuesday acted on more than 100 pieces of legislation, vetoing bills that would ban firearms for certain criminals, raise the smoking age, and preserve nonprofit hospitals' property-tax exemption.
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